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"Weapon" can refer to either the manufactured weapons used by dwarves and other creatures for either combat or specific labors, or natural weapons like fists, horns and breath attacks used for creature-specific methods of combat.

These weapons are constructed by dwarves or other intelligent races. There are many types of weapons, but not all may be manufactured in Fortress Mode. For notes on how to create weapons see Metalsmith's forge.

If you find your dwarves wearing more than one weapon -- or any unwanted armor, for that matter -- one way to get rid of them is to dump the weapon from their v-i inventory screen. This does not always work, as they might re-equip the item. Another option is to remove any weapons and/or shields listed on their military equip screen. This too does not always work. At least "left-handedness" seems to not pose a problem. If you cancel the work by v-p and selecting a job that needs a tool they will sometimes put it back in the pile. Example: Miners use picks, cancel their mining job and they will put the pick away AFTER you ordered it to be dumped.

Using weapons is much more effective than unarmed combat -- an untrained swordsdwarf with an iron weapon can defeat a grand master wrestler, provided neither is wearing armor.

Larger weapons with more heft tend to do more damage. How damage is calculated is currently not fully understood, and this is an area requiring more research.

Weapons and ammunition with the "foreign" attribute (item being rarer than Common in the entity file) must be either imported by either traders or invaders, or acquired from strange moods.

Weapons originating from strange moods can be made from almost any material: while it is never normally possible to manufacture a bone spear, for example, a fey bone carver may produce one from a single rainbow trout bone.

Training weapons are all wooden, and all made at the carpenter's workshop. All Battle axe, Spear, and Short Sword training weapons can be constructed in dwarf fortress mode.

Crossbows can be made of metal, wood, and bone. Metal crossbows are made by a weaponsmith at a forge, while wood and bone crossbows are made by a bowyer at a bowyer's workshop. The material of a crossbow does not affect its firing ability, only its melee damage. A dwarf's marksmanship skill is only affected by the core quality of the bow. This may be a consideration when deciding which dwarf you want outfitting your marksdwarves: a legendary bowyer is a better choice than a proficient weaponsmith.

The size for a weapon is its volume in cm3.

Attacks of type EDGE will either slice or pierce their target, depending on the contact area and penetration depth, while BLUNT attacks tend to damage internal organs without necessarily causing significant damage to outer layers.

The contact area represents the area of contact of the weapon, and the penetration determines how deep the attack goes (and is apparently ignored entirely for BLUNT attacks -- indicated by numbers in parentheses). Large contact areas combined with low penetration represent slashing attacks, while small contact areas with high penetration behave as piercing attacks.

The velocity seems to adjust the amount of actual force used during the attack (otherwise based on the size of the weapon, the material from which the weapon is made, and the strength of the wielder) - for example, war hammers have a 2x velocity multiplier, presumably to model the fact that the hammer's mass is concentrated at the tip which, when combined with a long handle, permits swinging it harder than a weapon whose mass is evenly distributed (such as a sword).

In fortress mode, foreign weapons can only be constructed by a dwarf experiencing a strange mood, out of any material. They may also be acquired from other races through trade or looting. Elves construct these out of wood, while other races construct them out of metal. Many dwarf-made weapons can be made by foreign civilizations as well, the Used by column is in no way all the weapons that race can make.

Using any multigrasp weapon in a single hand (ie. with a shield in the other hand) gives you a disability to hit.

Combat information is used internally by the game to determine the combat properties of weapons and armor made from this metal:

Density: Used in conjunction with other factors - heavier weapons (higher numbers) hit with more force, light weapons tend to have less penetration. Value shown here is g/cm3, which is the raw value divided by 103

Impact yield: Used for blunt-force combat; higher is better. This is the raw value divided by 103 (i.e., kPa).

Impact fracture: Used for blunt-force combat; higher is better. This is the raw value divided by 103 (i.e., kPa).

Impact elasticity: Used for blunt-force combat; lower is better. This is the raw value.

Shear yield: Used for cutting calculations in combat; higher is better. This is the raw value divided by 103 (i.e., kPa).

Shear fracture: Used for cutting calculations in combat; higher is better. This is the raw value divided by 103 (i.e., kPa).

Shear elasticity: Used for cutting calculations in combat; lower is better. This is the raw value.

General Term Explanations (From Wikipedia)

Yield Strength - The stress at which material strain changes from elastic deformation to plastic deformation, causing it to deform permanently.

Fracture Strength - The stress coordinate on the stress-strain curve at the point of rupture.

Stress - Force per area = F/A

Strain - Deformation of a solid due to stress = Stress/Young's Modulus

So...

Explanations!

Yield Strength is the amount of stress required to permanently deform (bend) a material (plastic deformation)

Fracture Strength is the amount of stress required to permanently break (rupture) a material

Elasticity (or IMPACT_STRAIN_AT_YIELD in RAWs) is the amount of deformation (bending) that occurs at the yield point

Implications to Dwarf Fortress Combat

Yield combined with Elasticity can tell what a material will do under stress (be it from a hammer, axe, or arrow)

Higher yield means that it takes more stress to deform

Lower elasticity means that it will deform less when stress is applied

Preliminary Combat Testing & Analysis

Adamantine and Steel take first and second place respectively, with Iron the third best material in the game. Beyond which, bronze is in a close tie with copper as to being the second worst material. As in older versions, silver continues to hold steady as the worst material available (no longer beneficial with wooden training weapons being available now) in regards to edged weaponry.
Additionally, with regards to blunt weapons almost all of the non-adamantine materials perform equally well, with a very slight edge towards steel and silver. Here is the thread with the details:

Keep in mind with how unbelievably complicated this system is nothing should be taken as word of law yet.

Best

Better

Good

Fair

Poor

Terrible

Notes

Armor

Adamantine

Steel

Iron

Bronze, Bismuth Bronze

Copper

Edged Weapons

Adamantine

(worst for missiles)

Steel

Iron

Bronze, Bismuth Bronze

Copper

Silver

For piercing iron armor, copper is better than bronze. For piercing copper or bronze armor, bronze is better than copper.

Blunt Weapons

Steel, Silver

Copper, Bismuth Bronze, Bronze, Iron

---

---

---

Adamantine

All six non-adamantine metals perform nearly identically. Steel has a slightly higher rate of critical wounds, while silver is slightly more likely to penetrate armor.

Cross refrencing this table with the table at the top of this section seems to indicate that low densities, high impact fractures, and high shear fractures contribute to the killing power of edged weapons.

Testing of weapons (15 dwarfs vs 15 dwarfs combats) shows that, in v0.31.12, the best dwarven-made weapon against humanoids is the silver war hammer.
Even in 15x(steel armor+silver war hammer) versus 15x(adamantine armor+adamantine battle axe) matches, hammerdwarves won with less than 50% casualties (mostly one-strike kills). However, when the dwarves in question were without armor or only wearing leather/cloth, the result was inverted - axedwarves won with less than 50% casualties. In battles against megabeasts, 6 silver hammerdwarves were barely able to scratch a bronze colossus (attacks were glancing away) due to bronze being a better "weapon" material.

This is because silver has the highest solid density of all materials that can regularly be made into weapons by dwarves. Tests show that indeed gold and platinum (increasingly dense) do increasing amounts of damage, and that war hammers remain the tool of choice, however they can only be produced by a moody dwarf (and a very lucky one at that).

Ammunition is fired from ranged weapons like crossbows and blowguns, and is stored in ammunition stockpiles, sometimes in quivers. Ammunition may also refer to the stones and ballista arrows fired from siege engines: For more information about these weapons, see the siege engine article.

Dwarves can become attached to a weapon, even a low quality weapon, which can make it difficult or impossible to get them to upgrade later.

In addition, the game tracks kills not only by entity but also by weapon. A weapon that has racked up enough kills might be named by its wielder. When this happens the game will pause and bring up a dialog box, similar to discovering a new cavern. Once named, the weapon will appear in the artifact list, albeit in blue.

Natural weapons are incredibly varied, but may be divided into a few basic types. Every creature in the game has natural weapons of one sort or another. (Even if one mods the attacks out, the creature will push as an attack.) A short description of natural weapons and damage considerations follows.

Every creature has basic natural weapons, most commonly biting and kicking. Damage done by these weapons depends greatly on the respective size of the combatants and the strength and striking/kicking/biting skill of the attacker.

Natural weapons in this category can include but are not limited to punching with the fists, biting with the teeth, goring with the horns, scratching with the nails, and kicking.

The various syndrome delivery methods fall under this category, including breath weapons, poisonous blood, area dusting, venomous bites, and so on. With the exception of some breath weapons, these attacks do not rely on size for damage calculation. For more information, see the syndrome page. For specific information on breath weapons, see the breath attacks section of the syndrome page.